The present invention relates to a sheet feed/discharge roller mechanism utilized in a printer, a photocopier or similar equipment.
A paper conveyance roller mechanism used in printers or photocopiers is generally placed on either the paper feed side or the paper discharge side of the unit and includes driving rollers and driven rollers, which revolve as a result of being in contact with the driving rollers. Generally, driven rollers are placed in contact with driving rollers by using one of two approaches. In the first approach, the driven rollers are mounted on a common shaft and biased towards the driving rollers by a common spring that acts on the common shaft. In the second approach, each of the driven rollers are individually biased towards a respective driving roller by a separate respective spring without the benefit of a common shaft.
However, both of the above-described roller mechanisms have difficulty conveying a narrow and thick recording sheet, such as a post card. When a narrow and thick recording sheet is inserted into the roller mechanism where the driven rollers are all connected to a common shaft and pushed by a common spring, the biasing force, which is set to bias all rollers for a full paper sheet, is excessive for the thicker post card. As a result, depression marks may form on the portion of the recording sheet (post card) if it is depressed excessively by an edge of an inner roller of the roller mechanism. Also, the recording sheet may not be conveyed evenly because of the unbalanced conveyance force generated by such a roller mechanism. When a narrow and thick recording sheet, such as a post card, is inserted into the second type of roller mechanism, the recording sheet may not be conveyed evenly because of a disparity of contact positions between the individual driven rollers and the recording sheet. Accordingly, it is desired to provide a biasing system which can provide even feeding, without depression marks for both wide thin recording sheets (paper) and narrow thick recording sheets (post cards).